Project Summary In professional baseball, a batter has ~400 ms to categorize an incoming fastball as playable or unplayable, leaving only a fraction of a second to rapidly modify the ongoing motion of the bat in order to successfully strike the target (i.e., baseball). While numerous studies have investigated the oculomotor system?s role in the visual categorization process, few have done so when the response must be initiated in advance of relevant sensory information, similar to the aforementioned example. Thus, the temporal dynamics of categorical influences on saccadic choices remain largely unresolved. To identify the manner in which visual categorization informs ongoing motor plans, I propose recording neural activity from populations of neurons in the lateral intraparietal area (LIP), frontal eye field (FEF), and superior colliculus (SC) while monkeys perform a task in which motor planning always precedes the identification of the visual stimulus; consequently revealing the temporal evolution of a categorical judgment with millisecond resolution. Results from prior studies identified neurons in LIP, and FEF that demonstrate categorical tuning, with increased firing rates when stimuli belonging to the preferred category appear on screen. Additionally, pilot data from our lab demonstrates the causal role of LIP in visual categorization; reversible inactivation of LIP leads to significant deficits in categorization accuracy. Yet, these studies make no attempt at uncovering the manner in which categorical signals influence ongoing motor plans, or identify differences in the timing and strength of categorical encoding between these brain regions. To date, no study has investigated categorical encoding in the SC, thus we will be the first to identify its role in visual categorization. By recording from large, diverse populations of neurons -simultaneously across these three interconnected brain regions- the proposed research will provide critical insight into the temporal dynamics underlying the transformation of sensory evidence into oculomotor choice.